Team Zeroes In On Cameroon Disaster Theory

September 14, 1986|The New York Times

WASHINGTON -- A team of scientists from the United States, in a preliminary report, has suggested four causes for the poisoning last month of more than 1,700 people who lived near a volcanic lake in northwestern Cameroon.

The study was prepared for the Agency for International Development by a seven-member team of volcanologists, environmental engineers and geologists.

Days after the disaster at Lake Nios on Aug. 21, scientists believed that it was caused by a geological disturbance miles beneath the volcano that caused hot volcanic gases to pierce a huge bubble of carbon dioxide beneath the lake`s surface.

The team offered this as one of the explanations for the disaster, but said it was probably not correct. The scientists said surveys of the lake bottom found no evidence that sediments had been disturbed.

The team also considered two other scenarios involving the injection of volcanic gases into a bubble of carbon dioxide suspended in the mud or rock beneath the lake`s bottom. But the evidence that the waters near the bottom were free of sediments indicated there had not been a disturbance in the sediments.

A more likely explanation, according to the study, was the sudden ``overturn`` of cold water near the lake`s bottom with warmer water near the surface. Warm water is less dense than cold water, the study explained. In a lake, warm and cold water will form distinct layers, or stratification.

The team suggested that the deep water may have contained large amounts of carbon dioxide. In the rainy season, air and surface waters are cooler, reducing the density difference between the water on the surface and the water on the lake`s bottom, and thereby requiring less energy to overcome stratification and mix Lake Nios`s water.

``A complete mixing is called an overturn,`` the study said, ``and if deep water contains large amounts of carbon dioxide, an overturn could cause a catastrophic release of this gas.``

The team urged Cameroonian scientists to begin determining the amount of carbon dioxide in these lakes and to develop other monitoring systems.

THE IDEAS

MOST LIKELY CAUSE

-- The sudden ``overturn`` of cold water containing large amount of carbon dioxide near the lake`s bottom with warmer surface water.

LEAST LIKELY CAUSES

-- A geological disturbance miles beneath the volcano that caused hot volcanic gases to pierce a huge bubble of carbon dioxide beneath the surface.

-- Two theories involving the injection of volcanic gases into a bubble of carbon dioxide suspended in the mud or rock beneath the lake`s bottom.